1. Field of the Invention
The present disclosure relates to a method for increasing the solid content of catalytic cracking catalyst slurry, which is suitable for preparation of catalytic cracking catalyst in petroleum processing. The method may be used to significantly boost the solid content of a catalyst slurry during catalyst preparation.
2. Background of the Invention
Fluidized Catalytic Cracking (abbreviated as FCC) is a major component in the secondary processing of crude oil. Deep processing of heavy oil via FCC is an important means for manufacturing vehicle fuel both at home and abroad. Due to increasing densification and degeneration of raw materials available for processing along with the rising demand for vehicle fuel, the consumption of FCC catalyst continually increases. Meanwhile, due to the requirement of heavy oil processing and FCC technology development, the proportion of molecular sieve active component in FCC catalyst has tended to increase. Generally the technological process for preparing semisynthetic FCC catalyst is to make a slurry of adhesives (such as aluminum collosol), pseudoboehmite, clay, inorganic acid and molecular sieve, etc., and then obtain catalyst product by spray molding and post treatment. Presently, there are such problems in the preparation methods as low colloid solid content before spray molding, and non-uniform mixing of molecular sieve active component and other components (called matrix components), etc. These problems result in high cost of catalyst production, uneven particle size of molded microbeads, poor sphericity and/or inadequate thermostability of active catalyst center such that molecular sieves of the catalyst fail to enable top catalyst reaction performance. According to conventional preparation processes, an increase of the solid content of the catalyst slurry will result in a much higher viscidity of the slurry, which leads to delivery difficulties and less desirable anti-friction of the catalyst. These slurries, therefore, may not satisfy utilization requirements.
The prior art discloses various processes which address these problems. For example, U.S. Pat. No. 4,476,239 and U.S. Pat. No. 4,443,553 disclose a method for preparing a cracking catalyst. The method is characterized in that a dispersant of [Al2(OH)6-yCly]x or Al2(OH)5NO3 is added to the catalyst slurry to reduce the viscidity thereof and to increase the solid content of the sprayed catalytic slurry. According to these patents, in the absence of dispersants, the catalyst slurry containing aluminum base binder, clay, silicon source and molecular sieve has a solid content in a range of 20˜25%, while, after the addition of the said dispersants, the solid content can reach 30%. The disclosed preparation procedure is: water→pseudoboehmite→acidification→kaolin→molecular sieve→ammonium polysilicate→dispersant→beating to homogeneous→spray drying.
China Patent No. CN 1032498A introduces a method for preparation of semisynthetic fluid catalytic cracking catalyst, wherein, before drying the catalyst, PAM (polyacrylamide) with molecular weight of 2,500,000-5,000,000 units in an amount of 0.01%˜0.15% based on dry catalyst basis is added into the sprayed slurry as a dispersant. In this way, viscosity of the catalyst slurry can decrease 10%˜50% and catalyst output can increase without adversely influencing catalyst performance.
China Patent No. CN1081219C discloses a process to raise the solid content of a sprayed catalyst slurry. The process includes beating the molecular sieve slurry, aluminum collosol, pseudoboehmite, clay and inorganic acid. The process is characterized by the addition of molecular sieve prior to the addition of clay and inorganic acid; inorganic acid addition following addition of aluminum collosol; and preferable addition of the inorganic acid after the addition of aluminum collosol and pseudoboehmite. The method can increase the solid content of the catalyst slurry before spray drying.
China Patent No. CN1081218C also discloses a process to raise the solid content of a sprayed catalyst slurry. The process includes beating the molecular sieve slurry, aluminum collosol, pseudoboehmite, clay and inorganic acid so as to obtain a solid content of 25%˜45% in the slurry. The process is characterized by addition of aluminum collosol prior to the addition of clay and inorganic acid; addition of molecular sieve slurry after the addition of inorganic acid; and preferable addition of inorganic acid after addition of aluminum collosol and pseudoboehmite. This method may also increase the solid content of the catalyst slurry before spray drying.
China Patent No. CN1160436C discloses a method for preparing a cracking catalyst. The method includes beating the molecular sieve slurry, pseudoboehmite, clay and inorganic acid to homogeneity, with or without the addition of aluminum collosol, to obtain a catalyst slurry. The slurry is then spray dried. The method is characterized by the addition of a quantity of inorganic acid into a collosol of pseudoboehmite, the quantity depending upon the viscosity of the catalyst slurry. The method provided by this patent can avoid the changes of catalyst intensity and pore volume that results from unstable acid consumption by pseudoboehmite.
China Patent No. CN1119390C discloses a process to raise the solid content of a sprayed catalyst slurry. In this process, molecular sieve and/or aluminum collosol are added prior to the addition of clay and inorganic acid; inorganic acid is added after the addition of aluminum collosol, preferably, the inorganic acid is added after the addition of aluminum collosol and pseudoboehmite. There is no particular requirement for the addition sequence of the other materials. Furthermore, a dispersant such as ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate (DAP; or ammonium phosphate, dibasic) or a mixture thereof is added into the spray slurry so as to significantly increase the solid content and shorten the gel forming time.
Currently, the preparation of FCC catalyst of collosol aluminum complex binder comprises acidification of pseudoboehmite. The production process introduced in both domestic and overseas patent reports adopts the technical procedure of adding acid subsequent to addition of pseudoboehmite (e.g. U.S. Pat. No. 4,476,239; China Patent Nos. 1081218C and 1098130A, etc.). According to current acidification methods, catalyst slurry so prepared may have a solid content within 25%˜50%. One of the more prominent problems at the moment is that, because the inorganic acid is added after the addition of pseudoboehmite, the reaction between the inorganic acid and the pseudoboehmite is difficult to conduct homogeneously. Thus, excessive reaction is present in some regions and this leads to rapid increase of the slurry viscosity. A second prominent problem is the previously inevitable partial damage to the molecular sieve when inorganic acid is added after the addition of molecular sieve slurry. Concurrently, because system acidity cannot be adequately controlled at a low level (generally pH less than 2.8), it is difficult to fine the pseudoboehmite. In instances where the molecular sieve content is high (for instance, greater than 40%), the anti-friction of the catalyst is reduced and catalyst utility is significantly adversely affected.
Accordingly, there is a need for a new method of FCC catalyst preparation that raises the solid content in the spayed slurry, produces a uniform mixture of molecular sieves and matrix components, and shortens the preparation of FCC catalyst. Such a method will enhance the production efficiency and improve the catalyst performance. The method should retain or improve the anti-friction performance and the reactivity of the catalyst.